This protective helmet (10) comprises an inner cap (12), an outer cap (16) and a decoupling layer (20) capable of allowing the outer cap (16) to rotate relative to the inner cap (12) about any axis of rotation in the event of an impact, at least one spherical surface (39) being completely contained in the decoupling layer (20). The helmet (10) comprises a fastening strap (40) attached at two opposing points (42) of the inner cap (12) without any mechanical connection with the outer cap (16), the strap (40) being intended to fasten the helmet (10) to the head (14) of the wearer. The helmet (10) comprises a fastening frame (44) attached to the inner cap (12), the strap (40) being attached to the inner cap (12) by means of the fastening frame (44).